Should this plugin work with SSL? Does it work with Google or other know SMTP servers?

4/10 22:36 [22110] - warn: [plugins/load] The following plugins may not be compatible with your version of NodeBB. This may cause unintended behaviour or crashing. In the event of an unresponsive NodeBB caused by this plugin, run ./nodebb reset -p PLUGINNAME to disable it.

I had to ensure my keys in redis for SMTP username and password contained the proper creds. It seems like the admin page doesn't write back to the proper keys when saving the data ... and when the plugin runs, it pulls from the wrong keys. If you're using redis - check the key settings by starting redis-cli and then inspecting:
hget config emailer:local:username
hget config emailer:local:password

[plugins/load] The following plugins may not be compatible with your version of NodeBB. This may cause unintended behaviour or crashing. In the event of an unresponsive NodeBB caused by this plugin, run ./nodebb reset -p PLUGINNAME to disable it.